Magnetically recyclable hydrothermal biochar functionalized with β-CD for simultaneous capturing of cationic methylene blue and auramine O in wastewater

The highly efficient and recoverable magnetic hydrothermal biochar (β-CD@MHBC) was prepared by combining red sandalwood and β-cyclodextrin, and was used for removing methylene blue (MB) and auramine O (AO) dyes in the single and binary systems. The physical and chemical properties of the β-CD@MHBC were characterized using SEM-EDS, BET, XRD, VSM, FT-IR, and XPS techniques. Batch adsorption studies revealed that the obtained maximum adsorption capacities of β-CD@MHBC for MB and AO in the single system were 303.1 and 400.0mgg-1, while in the binary system were 151.1 and 169.1mgg-1 under the optimal conditions of pH 6, 1.0gL-1 dosage, 150mgL-1 dye concentration and adsorption time of 180min, indicating the presence of competitive adsorption with AO possessing stronger affinity in the binary system. The adsorption behaviors of MB and AO could be well described by the Langmuir isotherm model and pseudo-second-order kinetic model in both single and binary systems. The possible adsorption mechanism involved pore filling, electrostatic attraction and hydrogen bonds between β-CD@MHBC and dye molecules. Furthermore, the spent β-CD@MHBC displayed excellent reusability and stability with removal efficiencies of 94% for MB and 83% for AO after five cycles of adsorption-desorption. In summary, the prepared β-CD@MHBC with excellent adsorption property and regeneration performance could have great potential for continuous removal of target pollutants in actual wastewater treatment.